1. Field of the Invention
The present invention relates to a developing device for use in an image forming apparatus such as a laser printer, etc., for developing an electrostatic latent image by supplying toner to the electrostatic latent image formed on an outer peripheral surface of a photosensitive drum and transferring the image developed on the surface of the photosensitive drum onto a sheet, and particularly to a developing device in an image forming apparatus capable of supplying toner which is supplied through a toner supply port formed in the developing device on a supply roller so that constantly fresh toner may be stuck uniformly on all over the supply roller, thereby capable of forming the image excellent in quality, for a long period.
In addition, the present invention relates to a developing device for use in an image forming apparatus such as a laser printer, etc., for developing an electrostatic latent image by supplying toner to the electrostatic latent image formed on an outer peripheral surface of a photosensitive drum and transferring the image developed on the surface of the photosensitive drum onto a sheet, and particularly to a developing device for use in an image forming apparatus, capable of smoothly supplying toner supplied from a toner storing part through a toner supply roller to a developing roller without causing toner clogging of a toner supply path formed around the toner supply roller and the developing roller, thus for a long time obtaining the resultant image excellent in quality.
2. Description of Related Art
Regarding conventional developing devices for use in image forming apparatuses such as laser printers, etc., there have been proposed various types of the devices, wherein the developing devices are often constructed in a unit type to be attachably mounted in a laser printer. Such a developing device is usually provided with an exchangeable toner cartridge for storing therein toner, and a toner supply port constructed of an opening for toner supply formed at a substantially center position of the toner cartridge in its width direction and another opening for toner supply formed in a frame of the developing device, through which toner is supplied.
One embodiment of the developing device will be explained with reference to FIG. 10. FIG. 10 is an explanatory view showing schematically a main construction of the developing device in the prior art.
In FIG. 10, the developing device has a toner cartridge 100 which accommodates therein toner and is provided with an opening for toner supply at an almost center in its width direction. This toner cartridge 100 is provided therein with an agitator 103 for agitating toner to supply same into a developing chamber 102 side through a toner supply port 101. A frame F of the developing device is provided with an opening for toner supply positioned corresponding to the toner supply opening of the toner cartridge 100. Those openings of the toner cartridge 100 and the frame F form the toner supply port 101 in combination with each other.
Inside the developing chamber 102 defined by an upper frame F1 and a lower frame F2 of the frame F, a toner supply roller 104 is arranged rotatably in a lower frame F2 side, for supplying the toner supplied through the toner supply port 101 to a developing roller 105. On an internal wall of the upper frame F1, above the developing roller 105, a blade 107 is fixedly secured with a fixing element 106, whereby to regulate a thickness of toner layer formed on the surface of the developing roller 105. This developing roller 105 is also arranged in contact with a photosensitive drum 108. On the peripheral surface of the photosensitive drum 108 is formed an electrostatic latent image by an image exposure device not shown which performs a scanning operation with a laser beam in accordance with image data. The developing roller 105 supplies toner on the electrostatic latent image formed on the peripheral surface of the photosensitive drum 108 to develop the image. The image developed on the surface of the photosensitive drum 108 is then transferred onto a sheet fed from a sheet feeder not shown, forming a resultant image, i.e., a visual image on the sheet.
In the toner cartridge 100 of conventional developing device mentioned above, however, toner would drop from and scatter outside the toner cartridge 100, for instance, in exchanging the toner cartridge 100. Such the toner scattering may cause toner sticking on other components of the laser printer and thus contamination of those components. To prevent the toner scattering, the conventional toner cartridge 100 is generally provided with only one toner supply port 101 at an almost center position in the width direction of the toner cartridge 100, i.e., in a vertical direction with respect to the drawing paper of FIG. 10, also corresponding to the width direction of the laser printer.
Accordingly, during a toner supplying operation to supply toner from the toner cartridge 100 to the developing chamber 102 through the toner supply port 101, the toner often tends to remain in the center portion of the toner supply roller 104. This causes a shortage of toner to be supplied to both side portions of the toner supply roller 104. In this case, it is impossible to supply toner uniformly to all over the toner supply roller 104, resulting in uneven toner supply with respect to the developing roller 105 and thus the electrostatic latent image formed on the photosensitive drum 108. As a result, the resultant image on the sheet would uneven in density, namely, dark in a center part on the sheet and pale in both side parts on the same, thereby causing a problem of a deterioration in image quality.
Furthermore, to solve the aforesaid problem that unevenness in the image density occurs due to ununiform supplying and sticking of toner onto all over the toner supply roller 104 in the toner cartridge 100 of the conventional developing device mentioned above, there may be provided an auger roller 109 (FIG. 11), for example, which is arranged rotatably above the toner supply roller 104, for circulating the toner supplied from the toner supply port 101 in a predetermined direction. With this auger roller 109, toner can be transported and circulated above the toner supply roller 104 inside the developing chamber 102, thereby enabling uniform supplying and sticking of toner to the toner supply roller 104.
However, there may occur a problem that such the auger roller 109 disposed above the supply roller 104 blocks a smooth flow of toner along the toner supply path formed around the toner supply roller 104 and the developing roller 105, thus causing the toner supply path to be clogged with the toner. If a toner clogging in the toner supply path occurs in such a way, it prevents appropriate supply of toner from the toner supply roller 104 to the developing roller 105, which would cause an extreme deterioration in quality of the resulting image obtained by developing the electrostatic latent image formed on the photosensitive drum 108. It is therefore difficult to continuously form the image excellent in quality.